A70-year-oldmancomplains of the sudden onset of visual loss in his right eye accompanied by a headache. He has a history of hypertension and diabetes mellitus. On physical examination, visual acuity in the left eye is 20/20 while visual acuity in the right eye is 20/90. Funduscopic exam shows the right disc to be pale and swollen with some hemorrhages. Which of the following is the most likely diagnosis?